Fix bug: error:file-operation couldn't work properly.

Fix bug: error:file-operation couldn't work properly.

This is because substitutable-value-condition-signaller was mis-designed.  It
added retries *after* building the condition, so they weren't in the condition
and would never be shown.

I rewrote error:file-operation based on the model in microcode-errors.scm which
was apparently a workaround for the fact that error:file-operation didn't work.

This entailed a small but incompatible change to the procedure's arguments.